EDIT:  Since I created this tutorial I have discovered that the interior dimensions of the sub is different than the DRSD.  It is smaller, and thus requires a slightly different approach.  All the JK subs use a case marked for the 1680 Rolex.  Only the dials are different.  So I've placed a note at the end about how to deal with that. So I've always been dissatisfied with the DG2813 and even less satisfied with a more expensive asian clone of a 2836 in a vintage Rolex sub.  They are both assembled by small Chinese children in a dirty factory and they have no lubrication in the movement.  To add insult to injury the 2836 clone is the wrong beat rate, and is more expensive.  Still crap.  If you get a low beat Swiss pulled out of some old watch then it needs service to be decent.  Swiss 2836 still have the wrong beat rate.  So enter the Seiko NH35.  Its a tank of a movement, still built by asians but in a clean factory with oil and QC.  Its got the right movement and is one of the most popular automatic movements in the world.  Purported to run for years through abuse and neglect.  Its got pretty much the right beat rate.  Only real beef anyone has with it is that its not quite as accurate as the vastly more expensive Swiss ETA 2836.  But it can be had for $35-40.  I searched the boards and found people talking about how it was a waste of time trying to swap these in.  Wrong hand size, need gasket fabricated, datewheel, etc.  I looked at the specs and found not much difference at all.  Hand sizes: NH35 150/90/21 DG2813 150/100/17 ETA 150/90/25 The case sizes, stem height, and movement height are very close as well.  When you figure in the plastic gasket the NH35 comes with its damn near a perfect fit.  So lets see how to do it.  I'm going to use my trusty old test DRSD.  Its had damn near everything smacked about on it.  Even got a countersunk Athaya crown.   So here is the NH35 with the plastic gasket it comes with.
  Here is the donor 2813 that came with the watch.  I use a single edge razor blade to carefully pry off the date wheel overlay.
Here are both movements, I've moved the overlay onto the NH35.
I glued the DWO onto the NH35 date wheel with a 5 minute epoxy.  I like to line up the 3 with the stem.
Lay the dial on to see how it fits.  Got some time to move it.
Hands are going to be the wrong size.  I'm just going to go to my BIG BOX O HANDS and pick the closest. (Note: you can just buy mercedes hands for the Seiko from several suppliers)
I ended up using the 22 for the sec hand, and had to broach minute hand to fit.  Just a bit.  Both the handsets and the movements probably have .5mm error margins so it was no big deal.
I put the dial on using double stick tape.

The tape actually serves a double purpose, it holds on the dial but also adheres to the back of the rehaut to keep the movement in place.
Hands on!
Movement seated, looks good but just a little loose in the case.
I'd measured all this stuff long before I started and ordered an appropriate gasket to snug it up.  I put it in before the stem was inserted.


All in!  Fits like a glove.

And, the finished product!
Thanks for watching! OK, here are the differences in dealing with the 1680 cases.  The plastic spacer on the NH35/36 is a bit too large for this case.   The solution for this is to snap the plastic case off the movement and use a dremel with a drum sanding bit to take the outer edge of the spacer down to size.  Take your time and for God's sake don't do this with the spacer still on the movement as you will get plastic dust inside the movement.  You need to take maybe 1/16 or so off to get it to fit.  Then snap it back on the movement.  After that all the other directions are the same.